WanaGo:KShips: Over the weekend we talked to a company at the Home Show about a gas radiator system (and whole house was somewhere around 8k estimate, can't dump that cash on system unfortunately), great looking system. $2k I think was the 28kw boiler and they have many customers who do radiators over a number of years to cut costs.
Back to DIY, I had been wondering if viable to build a second circuit to separate radiators for a wetback circuit (the pressure issues have always been of concern but proper design I presume would be fine). The Gas system if installed would kick in if the wetback system wasn't maintaining a decent temp (especially early morning when the fire is out). I like your idea about using valves and maybe have it on same system to switch between the 2 systems as needed. When reading the brochure the gas boiler does mention solar input so I wonder if can be used with wetback as well.
Thanks for this.
What was the company you talked to about the boiler, and $2K for 28Kw? Would be interested to talk to them.
Boiler assisting the wetback could be very helpful indeed.
andrewNZ: So from what I see, it appears you don't plan to use a hot water cylinder as your "tank". That in itself looks like an oversight. If you use a standard HWC then you can use an ajax valve with no problems. You have no potential overflow in the house (no worries about blocked overflow drain pipes) because vent doubles as the overflow and safety in the event of a boil or failed ajax valve.
You'd be surprised how effective a thermosyphon is. You'd also be surprised how restrictive a solenoid valve is. In fact I'd be surprised if it allowed any flow at all, because there is no water pressure to force it open.
You're already saying you don't think a thermosyphon will work and then you're adding one as a "safety feature".
Honestly, I could never recommend complicating a system as you plan to. You're gaining nothing other than the cool factor of controlling it with something you wrote, and adding so many points of failure and potential safety risks it's not funny.
Stan's drawing is exactly what you need. You could still use smarts to control room temps if you want to.